The easyest way to do it is in the first frame of the movie. There under the actions tab, you select 'load movie' and then you have to select that you wanna read from file. Be sure you select 'level 0' because otherwise it doesn't work. You text file must look like "&var1=blabla&var2=blablablabla&var3=idem' etc, etc.
when the file is loaded, you can set the variables with action script, like
'SetVariable't1'=var1.
You can also look at http://were-here.com there are tutorials and examples.
Good Luck